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A number of additives have been proven to improve the performance of vanadium redox flow batteries (VRFBs). Polyacrylic acid (PAA) is considered to be one of the promising candidates because of its beneficial effects on the stability of batteries. This paper studied the influence of PAA on viscosity, which is one of the electrolyte transport properties. The viscosity of VOSO4 + PAA + H2O ternary solution was measured at different temperature, ionic strength, and ionic strength fractions in the temperature range of 283.15 K–318.15 K. Several thermodynamic parameters of the PAA aqueous solution were calculated, such as the viscosity B-coefficients, the apparent molar volume of infinite dilution and the free energy of activation. In addition, two different semi-empirical prediction equations were established for ternary solution viscosity on the basis of the Eyring's theory, and the better one was determined through comparison. The average relative deviation is 0.74% between the predicted and the experimental values, which indicates this function can be used to predict the viscosity of VOSO4 + PAA + H2O ternary solution.

In this paper, a model for viscosity of high-concentrated additive (methanesulfonic acid) in vanadium electrolyte is reported. Methanesulfonic acid was evaluated as a possible stabilizing agent for the thermal precipitation of supersaturated V(V) solutions at elevated temperatures. Viscosity (η) of the ternary solution CH3SO3H + VOSO4 + H2O was measured between the temperatures 283.15 K and 318.15 K under atmospheric pressure. Based on the viscosity, viscosity B-coefficient, activation energy (Δμ0≠0) and Gibbs free energy of activation (ΔG≠) were further calculated. With the help of these paraments, a semi-empirical predicting function is established to estimate the viscosity of high-concentrated additive, i.e. methanesulfonic acid in vanadium electrolyte. AARD of this semi-empirical method is 0.22%, which demonstrates that viscosity estimation for high-concentrated ternary solution CH3SO3H + VOSO4 + H2O can be achieved.